Titanium is strong, light weight, corrosion resistant, and biocompatible. This unique combination of properties makes it a valuable natural resource well suited for numerous potential commercial applications. Titanium has been manufactured commercially since at least 1948 and is broadly used in the aerospace, medical, and military defense industries. For example, the U.S. Geological Survey, Mineral Industry Surveys on titanium, reports that approximately 67% of mill products and castings during 2011 were used in commercial and military aerospace applications. Yet, other industries where titanium's properties would be useful still rely heavily upon general purpose steel. Heavy dependence on steel is not surprising because producing titanium by conventional methods can be twenty times more expensive than producing steel. Much of this high cost is due to the indirect nature of known processes, which are time-intensive and require high amounts of energy, as illustrated and discussed with reference to FIGS. 1-4 below.
FIG. 1 illustrates a conventional titanium production method 100. At stage 101, FeTiO3, also referred to as ilmenite, a natural ore, is reduced to a titanium rich slag (TiO2-slag) and pig iron (pig Fe) by a carbothermal process. At stage 102, chemical extractive metallurgy processes are utilized to remove some unwanted impurities and produce an upgraded TiO2 (also referred to as synthetic rutile). At stage 103, synthetic rutile is chlorinated with chlorine under high temperature (typically in the range of 800 to 1000° C.) to form titanium tetrachloride (TiCl4). Two well-known commercial processes have been used to process TiCl4: Kroll and Hunter.
The Hunter process 104, as originally practiced and developed by metallurgist and professor Matthew Hunter at the Rensselaer Polytechnic Institute, involves reducing TiCl4 with elemental sodium in a sealed steel pot under high temperature (approximately 900° C.) and pressure, to form titanium sponge and molten sodium chloride. Subsequently, the Hunter process was updated to a two stage process. In stage one of an updated Hunter process 104, TiCl4 is reduced with sodium to TiCl2, discharged from the first reactor, and fed with molten salt to a second stage batch reactor (over a furnace and under inert gas atmosphere) where it is combined with molten sodium to complete reduction to titanium sponge. After the reaction completes and the sealed pot cools, salt is washed away with hydrochloric acid solution and then dried. While the Hunter process 104 can theoretically make highly pure titanium metal, it is inefficient, time consuming, and costly, and therefore impractical for many industries.
The Kroll process 105, was developed by Wilhelm Kroll as an alternative to the Hunter process 104, and is described in U.S. Pat. No. 2,205,854 (issued Jun. 25, 1940). According to the Kroll process 105, TiCl4 is reduced with magnesium metal at atmospheric pressure and temperatures above 800° C. An inert gas is employed with the magnesium reducing agent in the reactor. Chips of metal bored from the reactor are treated with water and hydrochloric acid to remove magnesium chloride (MgCl2). It has been reported that the Kroll process took nearly 10 years to scale-up into a commercial production process.
In more recent history, particularly the past 20 years, research has continued in attempts to identify more economical methods of producing titanium. FIG. 2 illustrates one such method known as the Armstrong process 200. This process 200 begins at stage 201, where ilmenite ore undergoes carbothermal reduction to Ti-slag and pig Fe, followed by chemical extraction at stage 202, and high temperature chlorination of upgraded synthetic rutile to TiCl4 at stage 203. Stage 204 is a continuous process for reduction of TiCl4 using molten sodium (Na) metal. Although the Armstrong process presents some advantages over the Hunter and Kroll processes, a number of challenges remain. In one aspect, the Armstrong process results in a Ti powder having the consistency of mini sponges, making subsequent processes, such as compacting and sintering, difficult. In another aspect, molten sodium is a costly material and regenerating Na (from NaCl) is an energy intensive process. Furthermore, the Armstrong process still requires TiCl4. Therefore, the benefits of the Armstrong process are limited.
Subsequent to Kroll and Hunter, methods have been developed that modify the number of steps required to process titanium. One example, illustrated in FIG. 3, is the FCC Cambridge process. Method 300 begins at stage 301 where ilmenite ore undergoes carbothermal reduction to Ti-slag and pig Fe followed by chemical extraction at stage 302. At stage 303, the FCC Cambridge process uses electrolysis to electrochemically reduce upgraded synthetic rutile to Ti sponge or powder.
In January of 2004, the U.S. Department of Energy and Oak Ridge National Laboratory (ORNL) released a report titled “Summary of Emerging Titanium Cost Reduction Technologies,” in which it identified and described sixteen emerging titanium reduction processes. Despite considerable effort and financial support, such efforts have not been widely adopted, nor proven to be commercially useful in many instances for a variety of reasons.
As described above, the existing technologies, including both commercial and developmental processes, can be broadly segmented into two groups: (1) processes employing reduction of TiCl4, and (2) processes employing reduction of TiO2 to indirectly produce titanium. The emphasis of research of reduction of TiCl4 has largely focused on optimizing the TiCl4 reduction process. The emphasis of research by reduction of TiO2, in contrast, has largely focused on avoidance of high-temperature chlorination. Nonetheless, both segments and related research still require chemical extractive processes to obtain the upgraded (highly refined) rutile feed to subsequent process steps—also a costly step.
None of the aforementioned methods provide a method of titanium production that adequately improves the economic viability of titanium metal. FIG. 4 illustrates typical costs associated with conventional production of titanium. Magnesium and sodium reduction processing (e.g., Hunter process 103 and Kroll process 104 of FIG. 1) represent approximately 66% of total production costs. Chlorination to form TiCl4 represents about 24% of the total production costs, with the remaining 10% attributable to production of upgraded rutile. Thus, there remains a need for a simplified and reduced cost method for the production of titanium metal.